JP5476123B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine.

  A spark plug for an internal combustion engine is attached to an internal combustion engine (engine) and used for ignition of an air-fuel mixture in a combustion chamber. Generally, a spark plug is provided on the outer periphery of an insulator having an axial hole, a center electrode inserted through the front end of the axial hole, a terminal electrode inserted through the rear end of the axial hole, and the insulator. A metal shell and a ground electrode provided at the tip of the metal shell and forming a spark discharge gap with the center electrode are provided.

  By the way, with the operation of the internal combustion engine, conductive carbon may adhere to the insulator surface. Here, in particular, if carbon adheres to cover the insulator front end surface around the center electrode, the current applied to the center electrode leaks to the metal shell through the carbon of the insulator front end surface, There is a risk that normal spark discharge cannot be performed (fire is lost). Then, the technique which generate | occur | produces the spark discharge which propagates along the insulator front end surface between both electrodes by arrange | positioning so that the front-end | tip part of a ground electrode may be made to oppose the side part of a center electrode ( For example, see Patent Document 1). According to this technique, carbon adhering to the insulator front end surface due to spark discharge can be burned out, and excellent antifouling resistance can be realized.

  However, in recent years, improvement in ignitability has been demanded in order to improve fuel efficiency and reduce emissions. Here, when the above technique is adopted, spark discharge is generated at a position relatively away from the center of the combustion chamber, so that the ignitability may be insufficient.

  Therefore, from the viewpoint of improving ignitability, the side surface portion of the ground electrode is disposed to face the tip portion of the center electrode, and a noble metal tip having a relatively small diameter is disposed on the opposite surface of the center electrode or the ground electrode. A technique for providing the image has been proposed (see, for example, Patent Document 2). According to this technique, the spark discharge can be generated at the center of the combustion chamber, and the heat of the spark (flame core) can be prevented from being drawn from the center electrode or the ground electrode.

  However, recently, from the viewpoint of environmental regulations, a direct injection engine is used to save energy and suppress emission of unburned gas. Such a direct injection engine is used in the spark discharge gap or in the vicinity of the spark discharge gap. Since the fuel is injected into the carbon, carbon tends to adhere to the tip of the insulator. Here, when the above technique is adopted, the ignitability can be improved, but the carbon adhering to the insulator front end surface can hardly be burned out. Therefore, the stain resistance is insufficient, and there is a risk of misfire.

  On the other hand, by arranging the tip edge portion of the ground electrode so as to face the tip edge portion of the center electrode, the spark discharge is generated at the center of the combustion chamber and the ignitability is improved. A technique that can be expected to burn out carbon adhering to the insulator surface has been proposed (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 10-50455 JP 2005-108795 A JP 2004-55142 A

  However, in various types of spark plugs, the arrangement position of the insulator tip with respect to the center electrode tip is different (for example, the outer diameter of the center electrode tip and the inner diameter of the insulator tip are equal or different). The tip of the insulator is close to the tip of the center electrode, or is in a separated state. That is, the technique described in Patent Document 3 that defines the positional relationship between the center electrode and the ground electrode has not been sufficiently studied for improving the fouling resistance. In this technique, the fouling resistance is improved in various spark plugs. There is a risk that improvement cannot be achieved. In addition, according to the technique, although the insulator is not fouled, a spark discharge occurs between the insulator and the ground electrode, and the effect of improving the ignitability may not be sufficiently exhibited. .

  The present invention has been made in view of the above circumstances, and provides a spark plug for an internal combustion engine having excellent ignitability and sufficient antifouling property regardless of the position of the insulator with respect to the center electrode. is there.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug for an internal combustion engine of this configuration includes a rod-shaped center electrode extending in the axial direction,
A substantially cylindrical insulator having an axial hole extending in the axial direction and the central electrode provided in the axial hole;
A substantially cylindrical metal shell provided on the outer periphery of the insulator;
A grounding electrode extending from the tip of the metal shell, the tip being bent toward the center electrode,
A spark plug for an internal combustion engine having a gap between the center electrode and the ground electrode,
All the tip portions of the ground electrode are outside the virtual outer peripheral surface formed by extending the tip outer peripheral surface of the center electrode along the axial direction, and the tip in the axial direction from the virtual surface including the front end surface of the center electrode And exist on the side,
When the first shortest distance between the tip of the center electrode and the tip of the ground electrode is a, and the second shortest distance between the tip of the insulator and the tip of the ground electrode is b The following expression is satisfied.

1.1 ≦ b / a ≦ 1.6
A noble metal portion such as a noble metal tip made of a noble metal alloy may be provided on the center electrode or the ground electrode. In this case, the noble metal portion constitutes a part of the center electrode and the ground electrode.

  According to the configuration 1, the tip end portion of the ground electrode is outside the virtual outer peripheral surface formed by extending the outer peripheral surface of the center electrode tip portion along the axial direction and includes the tip end surface of the center electrode. It is located on the tip side in the axial direction from the surface. Thereby, a spark discharge can be generated on the center side of the combustion chamber from the front end surface of the center electrode, and the ignitability can be improved.

  According to the present configuration 1, the first shortest distance that is the shortest distance between the tip of the center electrode and the tip of the ground electrode is defined as a, and the distance between the tip of the insulator and the tip of the ground electrode When the second shortest distance, which is the shortest distance, is b, 1.1 ≦ b / a ≦ 1.6 is satisfied. That is, the second shortest distance is configured to be 1.1 to 1.6 times the first shortest distance.

  Here, since the second shortest distance is set to be 1.1 times or more of the first shortest distance, when the insulator front end surface is not contaminated by carbon (normal time), the comparison is made. Spark discharge is likely to occur between the center electrode and the ground electrode having a short target distance without passing through the insulator. That is, in a normal time, it is possible to realize a spark discharge excellent in ignitability on the center side of the combustion chamber as described above.

  On the other hand, since the second shortest distance is set to be 1.6 times or less of the first shortest distance, when the insulator front end surface is fouled by carbon (at the time of fouling), it is insulated. Spark discharge can occur through the body. Thereby, the carbon adhering to the insulator can be burned out, and the stain resistance can be improved.

  That is, according to the present configuration 1, the first shortest distance a and the second shortest distance b are configured so as to satisfy the expression 1.1 ≦ b / a ≦ 1.6. Thus, a spark discharge can be generated without being transmitted through the insulator, and at the time of fouling, a spark discharge transmitted through the insulator can be generated between both electrodes. Thereby, excellent ignitability and improvement of antifouling property can be realized at once.

  When 1.1> b / a, that is, when the second shortest distance is less than 1.1 times the first shortest distance, a spark discharge is normally transmitted through the insulator. This may lead to a decrease in ignitability. On the other hand, when b / a> 1.6, that is, when the second shortest distance exceeds 1.6 times the first shortest distance, spark discharge is transmitted through the insulator at the time of fouling. It becomes difficult to generate, and there is a possibility that the stain resistance may be lowered.

  Configuration 2. The spark plug for an internal combustion engine of this configuration satisfies 1.5 ≦ b / a ≦ 1.6 in the above configuration 1.

  According to the above configuration 2, it is possible to achieve even better ignition performance while maintaining excellent antifouling properties.

Configuration 3. The spark plug for an internal combustion engine according to the present configuration has a virtual projection plane orthogonal to the axis in the configuration 1 or 2, and a tip opening portion of the shaft hole and a tip portion of the center electrode among the tip portions of the ground electrode. Projecting the nearest corner, and the corner projected onto the virtual projection plane,
A contact point when a first tangent line is drawn from the first edge located at one end of the projection corner to the projection shaft hole that is the tip opening of the shaft hole projected onto the virtual projection plane is first. 1 contact,
When a contact point when a second tangent line is drawn to the projection shaft hole from the second end edge portion located at the other end of the projection angle portion is a second contact point,
The length L of the first contact and the second contact along the outer periphery of the projection shaft hole on the ground electrode side is 40% or more of the outer periphery length of the projection shaft hole. It is characterized by.

  In addition, when the tangent line is drawn with respect to the projection axis hole from the first edge part and the second edge part, two tangent lines can be drawn respectively. The “tangent” and “second tangent” mean two tangents that do not intersect each other between the projection angle portion and the projection axis hole (the same applies hereinafter).

  According to the configuration 3, the ratio of the length L between the first contact and the second contact along the outer periphery of the projection shaft hole on the ground electrode side with respect to the outer periphery length of the projection shaft hole (“electrode” The “opposite ratio” is 40% or more. In other words, for 40% or more of the insulator located around the center electrode, spark discharge can be generated through the portion. Thereby, the range in which carbon can be burned out at the time of fouling can be made relatively wide, and the fouling resistance can be further improved.

  When a plurality of ground electrodes are provided, when the length between both contacts along the outer periphery of the projection shaft hole on the ground electrode side is determined for each ground electrode, the total length between both contacts is It may be 40% or more of the outer peripheral length of the projection shaft hole. However, if the part that forms the length between the two contacts for the other ground electrode overlaps with the part that forms the length between the two contacts for one ground electrode, Of the parts forming the length between the two contacts for the electrode, the parts overlapping the part forming the length between the two contacts for the one ground electrode are excluded, and then the two contacts for each ground electrode The length between is required. Therefore, the upper limit of the total length between the two contacts is equal to the outer peripheral length of the projection shaft hole, and the upper limit of the electrode facing ratio is 100%.

  Configuration 4. The spark plug for an internal combustion engine according to the present configuration has the length L of the first contact and the second contact along the outer periphery of the projection shaft hole on the ground electrode side in the configuration 3 described above. It is characterized by being 50% or more of the outer peripheral length of the shaft hole.

  According to the configuration 4, the range in which carbon can be burned out can be made wider, and the stain resistance can be further improved.

  Configuration 5. The spark plug for an internal combustion engine according to this configuration is characterized in that, in any one of the above configurations 1 to 4, the tip end portion of the shaft hole has a taper toward the tip end side in the axial direction.

  According to the configuration 5, the tip portion of the shaft hole is provided with the tapered detail that tapers toward the tip end side in the axial direction. Therefore, the annular portion of the insulator positioned around the center electrode is provided. The region (area) can be made relatively small. Thereby, the carbon adhering to the surface of the annular portion can be burned out efficiently with a relatively small number of spark discharges, and the stain resistance can be further improved.

  In addition, by adopting the present configuration 5, the diameter of the tip portion of the center electrode is also relatively reduced. However, if the diameter of the entire area of the center electrode is reduced, the heat drawing performance of the center electrode is degraded. There is a fear. Therefore, from the viewpoint of sufficiently ensuring the heat extraction performance of the center electrode, it is preferable to reduce the diameter of only the tip of the center electrode in accordance with the shape of the tip of the shaft hole.

  Configuration 6. The spark plug for an internal combustion engine according to this configuration is characterized in that, in any one of the above configurations 1 to 5, a chamfered portion is provided at the tip opening of the shaft hole.

  When spark discharge occurs along the surface of the insulator, there is a concern that a phenomenon called channeling in which the surface of the insulator is scraped into a groove shape may occur. A chamfered portion is provided at the tip opening, and the path of current flowing through the insulator surface can be dispersed. As a result, the occurrence of channeling can be more reliably prevented, and uneven wear of the center electrode due to spark discharge can be suppressed. As a result, the durability can be further improved.

  Configuration 7. The spark plug for an internal combustion engine of this configuration is characterized in that in any of the above configurations 1 to 6, a plurality of the ground electrodes are provided.

  According to the structure 7, it is possible to further widen the burnable range of the carbon adhering to the insulator surface. Thereby, the further improvement of stain resistance can be aimed at.

  Configuration 8. The spark plug for an internal combustion engine according to this configuration is characterized in that, in any one of the above configurations 1 to 7, the center electrode includes a noble metal portion at a tip portion thereof.

  The “noble metal portion” is composed of a single noble metal or an alloy containing a noble metal. Examples of the noble metal include platinum and iridium (hereinafter the same).

  According to the configuration 8, the center electrode includes the noble metal portion made of the noble metal alloy at the tip portion thereof. As a result, it is possible to improve the spark wear resistance and further improve the durability.

  Configuration 9 The spark plug for an internal combustion engine according to this configuration is characterized in that, in any one of the above configurations 1 to 8, the ground electrode includes a noble metal portion at a portion facing a tip edge portion of the center electrode.

  According to the above configuration 9, since the ground electrode includes the noble metal portion made of the noble metal alloy in the portion facing the tip edge portion (corner portion) of the center electrode, the spark wear resistance can be further improved. it can. As a result, the durability can be further improved.

  Configuration 10 The spark plug for an internal combustion engine according to this configuration is characterized in that, in any one of the above configurations 1 to 9, the center electrode includes a noble metal portion in at least a part of a portion facing the tip opening of the shaft hole. .

  According to the configuration 10, the center electrode includes the noble metal portion in at least a part of the portion facing the tip opening of the shaft hole. As a result, it is possible to suppress the wear on the side surface of the center electrode when a spark discharge is generated by transmitting the carbon between the two electrodes, and the durability can be further improved.

It is a partially broken front view which shows the structure of the spark plug of this embodiment. It is a partially broken enlarged view which shows the structure of the front-end | tip part of a spark plug. It is a schematic diagram which shows the axial hole, the ground electrode, etc. which were projected on the virtual projection surface. It is a schematic diagram for demonstrating a 1st tangent and a 2nd tangent. It is a graph which shows the result of an ignitability evaluation test. (A) is an expanded sectional view which shows the structure of the spark plug front-end | tip part in another embodiment, (b) is an expanded sectional view which shows structures, such as a shaft hole in (alpha) area | region of the same figure (a). . It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment. It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment. It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment. It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment. It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment. It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment. It is a partially broken enlarged view which shows the structure of the spark plug front-end | tip part in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially broken front view showing a spark plug (hereinafter referred to as “spark plug”) 1 for an internal combustion engine. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. On the side, a leg length part 13 formed with a smaller diameter than this is provided. Of the insulator 2, most of the large diameter portion 11, the middle trunk portion 12, and the leg long portion 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the leg length portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, the insulator 2 is formed with a shaft hole 4 penetrating along the axis CL1, and a center electrode 5 is inserted and fixed to the tip end side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Furthermore, the center electrode 5 has a rod shape (cylindrical shape) as a whole, and its tip end surface is formed flat and protrudes from the tip of the insulator 2.

  A terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface thereof. Yes. In addition, a seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the engine head is provided. A caulking portion 20 for holding the insulator 2 is provided.

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. Thereby, the air tightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  Further, a ground electrode 27 made of a Ni-based alloy is joined to the distal end portion 26 of the metal shell 3. Here, the ground electrode 27 has its rear end welded to the front end surface of the front end portion 26 of the metal shell 3, the front end side is bent back, and the side surface thereof faces the front end edge portion of the center electrode 5. The ground electrode main body portion 28 and a noble metal portion 31 made of a noble metal alloy (for example, a platinum alloy or an iridium alloy) joined to the tip of the ground electrode main body portion 28 are configured.

  In addition, the noble metal portion 31 is formed so that the width along the direction orthogonal to the axis CL <b> 1 is wider than the outer diameter of the center electrode 5. In addition, the noble metal portion 31 has a portion of one end portion of the noble metal portion 31 embedded in the side surface of the ground electrode body portion 28 on the center electrode 5 side, and the other end portion of the noble metal portion 31 from the front end surface of the ground electrode body portion 28. It is comprised so that it may protrude. A spark discharge gap 33 is formed as a gap between the tip of the ground electrode 27 (the noble metal portion 31) and the tip of the center electrode 5.

  Further, in the present embodiment, as shown in FIG. 2, it is outside the virtual outer peripheral surface KG formed by extending the front end outer peripheral surface 5G of the center electrode 5 along the direction of the axis CL1, and the front end surface of the center electrode 5 The distal end portion of the ground electrode 27 is configured to be closer to the distal end side in the axis CL1 direction than the virtual plane KS including

  In addition, the first shortest distance, which is the shortest distance between the tip of the center electrode 5 and the tip of the ground electrode 27 (the noble metal portion 31), is a (mm), and the tip of the insulator 2 and the ground electrode 27. When the second shortest distance, which is the shortest distance between the front end portion and b (mm), is 1.1 ≦ b / a ≦ 1.6 [that is, the second shortest distance Is configured to be not less than 1.1 times and not more than 1.6 times (for example, 1.3 times) of the first shortest distance]. In the present embodiment, a first shortest distance is formed between the corner portion 35 of the noble metal portion 31 and the tip portion of the center electrode 5, and the corner portion 35 of the noble metal portion 31 and the tip portion of the insulator 2 are formed. A second shortest distance is formed between them. That is, the first shortest distance and the second shortest distance are set to be the same as the base point on the ground electrode 27 side.

  Further, the center electrode 5, the ground electrode 27, and the like in the present embodiment have the following positional relationship. That is, as shown in FIG. 3, of the tip portion of the ground electrode 27, the corner portion 35 closest to the tip portion of the center electrode 5 and the tip opening portion of the shaft hole 4 are virtually projected perpendicularly to the axis CL1. Project onto the surface KT. And from the 1st edge part EG1 located in the end of the projection corner | angular part TC which is the corner | angular part 35 projected on the said virtual projection surface KT, the front-end | tip opening part of the said axial hole 4 projected on the virtual projection surface KT. The projection axis hole BP (part indicated by a bold line in the drawing) is drawn with a first tangent line SL1, and the projection axis from the second edge EG2 located at the other end of the projection angle portion TC. A second tangent line SL2 is drawn in the hole BP. At this time, the projection between the first contact SP1 that is a contact point between the projection shaft hole BP and the first tangent line SL1 and the second contact point SP2 that is a contact point between the projection shaft hole BP and the second tangent line SL2 are performed. The ratio of the length L along the outer periphery of the shaft hole BP on the ground electrode 27 side to the outer periphery length of the projection shaft hole BP (referred to as “electrode facing ratio”) is 40% or more (for example, 50%). .

  As shown in FIG. 4, when a tangent line is drawn from the first end edge part EG1 to the projection axis hole BP, two tangent lines sa1 and sb1 can be drawn. When a tangent line is drawn from the EG2 to the projection axis hole BP, two tangent lines sa2 and sb2 can be drawn. In the present embodiment, the “first tangent line SL1” and the “second tangent line SL2” are drawn. Means two tangents sa1 and sb2 that do not intersect each other between the projection angle portion TC and the projection axis hole BP.

  Next, in order to confirm the operational effects achieved by the present embodiment, the spark plug in which the ratio (b / a) of the second shortest distance to the first shortest distance was variously changed between 1.0 and 1.8. Samples were prepared, and each sample was subjected to an antifouling evaluation test and an ignitability evaluation test. First, the stain resistance evaluation test will be described. The test is a “smoldering stain test” defined in JIS standard D1606, and details are as follows. That is, a test vehicle having a 4-cylinder engine with a displacement of 1600 cc is placed on a chassis dynamometer in a low temperature test chamber (−10 ° C.), and a sample of each spark plug is assigned to each cylinder of the test vehicle engine. Assemble four. After performing idling three times, the vehicle travels for 40 seconds at a third speed of 35 km / h, and again travels for 40 seconds at a third speed of 35 km / h with an idling of 90 seconds. Then stop and cool the engine once. Next, after performing idling three times, traveling for 20 seconds at a speed of 15 km / h is performed a total of three times, with the engine stopped for 30 seconds, and then the engine is stopped. This series of test patterns was taken as one cycle, and the test was repeated 10 cycles. Then, at the end of 10 cycles, the insulation resistance value between the metal shell and the terminal electrode was measured for a predetermined spark plug sample. Here, when the measured insulation resistance value was 10 MΩ or more, “◯” was evaluated as being excellent in antifouling property. On the other hand, when the measured insulation resistance value was less than 10 MΩ, the evaluation of “x” was made because the stain resistance was insufficient.

  Next, in the ignitability evaluation test, each sample was assembled in a 6-cylinder DOHC engine with a displacement of 2000 cc, and the engine was rotated at 2000 rpm and a suction negative pressure of -350 mmHg to gradually increase the air-fuel ratio (A / F). The air-fuel ratio at the time of 1% misfire was measured as the lean limit air-fuel ratio. Here, when the lean limit air-fuel ratio is 22.0 or more, “◯” is evaluated as being excellent in ignitability, and when the lean limit air-fuel ratio is 23.5 or more, the ignitability is determined. It was decided to give a rating of “◎” as being very excellent. On the other hand, when the lean limit air-fuel ratio is less than 22.0, the ignitability is insufficient and “x” is evaluated. Table 1 shows the results of the fouling resistance evaluation test and the ignitability evaluation test. In particular, the results of the ignitability evaluation test are shown in the graph of FIG. In addition, about each sample, while the protrusion length from the insulator of the center electrode front-end | tip part was 1.5 mm, the outer diameter of the front-end | tip part of a center electrode was 2.0 mm.

表１に示すように、ｂ／ａの値が１．６を超えるサンプルは（サンプル８，９）は、絶縁抵抗値が１０ＭΩ未満となり、耐汚損性が不十分であることがわかった。これは、絶縁碍子の先端部と接地電極の先端部との距離が大きくなりすぎたため、両電極間で絶縁碍子を伝わっての火花放電が発生しづらくなってしまったことによると考えられる。

As shown in Table 1, it was found that the samples having a b / a value exceeding 1.6 (Samples 8 and 9) had an insulation resistance value of less than 10 MΩ, and the stain resistance was insufficient. This is considered to be due to the fact that the distance between the tip of the insulator and the tip of the ground electrode has become too large, so that it is difficult for spark discharge to travel between the two electrodes through the insulator.

  On the other hand, samples (samples 1, 2, 3, 4, 5, 6, and 7) having a b / a value of 1.0 or more and 1.6 or less have an insulation resistance value of 10 MΩ or more, which is excellent. It was revealed that it has stain resistance. This is presumably because when the tip end face of the insulator was fouled by carbon, spark discharge was easily generated between the two electrodes through the insulator and the carbon could be burned out.

  In addition, as shown in Table 1 and FIG. 5, it was found that the sample (sample 1) in which the value of b / a was less than 1.1 has insufficient ignitability. This is considered to be due to the fact that spark discharge is easily generated between the two electrodes through the insulator even when the insulator front end surface is not contaminated with carbon (normal time).

  On the other hand, it was revealed that samples (samples 2 to 9) having a b / a value of 1.1 or more and 1.8 or less have excellent ignitability. This is considered to be due to the fact that spark discharge is likely to occur between both electrodes without passing through the insulator in normal times. In particular, it was found that samples (samples 6 to 9) having a b / a value of 1.5 or more have extremely excellent ignitability.

  As described above, in order to realize both excellent antifouling resistance and excellent ignitability at once, considering the results of both evaluation tests comprehensively, the value of b / a is 1.1 or more. It can be said that it is preferably 6 or less. Moreover, it can be said that it is desirable to make the value of b / a into 1.5 or more and 1.6 or less from a viewpoint of aiming at the further improvement of ignitability, maintaining the outstanding fouling resistance.

  Next, the ground electrode of the projection shaft hole between the first contact and the second contact with respect to the outer peripheral length of the projection shaft hole is changed by changing the shape of the ground electrode and the center electrode and the number of electrodes of the ground electrode. Samples of spark plugs having various length ratios (electrode facing ratios) along the outer periphery on the side were prepared, and the above-described stain resistance evaluation test was performed on each sample. Here, when the insulation resistance value at the end of 10 cycles is 10 MΩ or more, the evaluation of “◯” is given as being excellent in antifouling property, and the insulation resistance value at the end of 11 to 15 cycles is 10 MΩ or more. In this case, it was decided to give an evaluation of “◎” because it was very excellent in stain resistance. Furthermore, when the insulation resistance value at the end of 16 cycles was 10 MΩ or more, “☆” was evaluated as being extremely excellent in antifouling property. In each sample, the value of b / a was set to 1.1 or more and 1.6 or less. In Samples 10 to 14, the number of ground electrode electrodes was 1, and in Sample 15, the number of ground electrode electrodes was 2. The results of the evaluation test are shown in Table 2.

表２に示すように、各サンプル（サンプル１０〜１５）ともに優れた耐汚損性を有することが明らかとなった。特に、電極対向割合が４０％以上のサンプル（サンプル１２〜１５）については、１０サイクルを超えた後においても、絶縁抵抗値が１０ＭΩ以上となり、非常に優れた耐汚損性を有することが認められた。これは、中心電極と接地電極との間における、火花放電可能な領域が比較的大きくされたことに伴い、カーボンを焼き切り可能範囲が比較的広くなったことによると考えられる。また、電極対向割合が５０％以上のサンプル（サンプル１３〜１５）については、１６サイクル以上に亘って、１０ＭΩ以上の絶縁抵抗値が保たれ、極めて優れた耐汚損性を有することがわかった。従って、耐汚損性の更なる向上を図るという観点からは、電極対向割合を４０％以上とすることが好ましく、電極対向割合を５０％以上とすることがより好ましいといえる。

As shown in Table 2, it was revealed that each sample (samples 10 to 15) had excellent antifouling resistance. In particular, for the samples having the electrode facing ratio of 40% or more (samples 12 to 15), even after exceeding 10 cycles, the insulation resistance value is 10 MΩ or more, and it is recognized that the sample has very excellent antifouling property. It was. This is considered to be due to the fact that the range in which carbon can be burned out is relatively wide as the spark dischargeable area between the center electrode and the ground electrode is relatively large. Moreover, about the sample (samples 13-15) whose electrode facing ratio is 50% or more, it turned out that the insulation resistance value of 10 M (ohm) or more is maintained over 16 cycles or more, and it has the outstanding stain resistance. Therefore, from the viewpoint of further improving the fouling resistance, the electrode facing ratio is preferably 40% or more, and the electrode facing ratio is more preferably 50% or more.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the tip of the shaft hole 4 is formed to have a substantially constant inner diameter, and the tip of the center electrode 5 is also formed to have a substantially constant outer diameter. . On the other hand, as shown in FIGS. 6 (a) and 6 (b) (note that FIG. 6 (b) is an enlarged sectional view showing the α region in FIG. 6 (a)) A tapered portion SB that tapers toward the tip end side in the axis line CL1 direction is formed at the tip end, and a center electrode 5 is formed in a tapered shape that tapers toward the tip end side in the axis line CL1 direction in accordance with the shape of the shaft hole 4. It is good as well. In this case, the region (area) of the annular portion located around the center electrode 5 in the insulator 2 can be made relatively small. Thereby, the carbon adhering to the surface of the annular portion can be burned out efficiently with a relatively small number of spark discharges, and the stain resistance can be further improved.

  Moreover, in the said embodiment, although the front-end | tip opening part of the shaft hole 4 is formed so that a cross section may become substantially right-angled, it is good also as providing the chamfer part MB in the front-end | tip opening part of the shaft hole 4. In this case, the occurrence of channeling can be more reliably suppressed, and as a result, durability can be improved. In the figure, the chamfered portion MB is formed in a curved surface shape, but may be formed in a tapered shape or the like.

  (B) In the above embodiment, the ground electrode main body 28 has a single-layer structure made of Ni alloy. As shown in FIG. 7, for example, the ground electrode main body 28 is composed of an outer layer 28A and an inner layer 28B. It is good also as comprising in 2 layer structure. Here, from the viewpoint of achieving good performance in terms of both durability and heat-drawing performance of the ground electrode main body 28, Ni alloy [for example, Inconel 600 and Inconel 601 (both registered) is used as the material for forming the outer layer 28A. In addition, it is desirable to adopt a copper alloy or pure copper, which is a heat conductive metal better than the Ni alloy, as a material for forming the inner layer 28B.

  (C) In the above embodiment, the tip end portion of the ground electrode main body portion 28 is formed so as to extend in the direction orthogonal to the axis CL1 (the left side in the figure). It is not limited. Therefore, for example, as shown in FIG. 8, the tip of the ground electrode main body 28 may be formed so as to extend obliquely upward in the drawing. For example, since the metal shell 3 has a relatively small diameter (for example, the screw portion 15 of the metal shell 3 is M10 or less), the joint between the metal shell 3 and the ground electrode 27 is formed. This is particularly significant when the ground electrode 27 is relatively difficult to bend when the spark discharge gap 33 is adjusted.

  Moreover, in the said embodiment, although the ground electrode 27 is comprised by the ground electrode main-body part 28 and the noble metal part 31 provided in the said ground electrode main-body part 28, as shown in the figure, the noble metal part 31 is comprised. The ground electrode 27 may be configured by the ground electrode main body 28 alone without providing the ground electrode. In this case, the corner portion 35 of the ground electrode 27 means the corner portion 35 a located on the insulator 2 side of the tip portion of the ground electrode main body portion 28.

  (D) In the above embodiment, only one ground electrode 27 is provided, but a plurality of ground electrodes 27a and 27b may be provided as shown in FIG. In this case, since the carbon can be burned out further, the fouling resistance can be further improved.

  (E) In the above embodiment, the noble metal portion 31 has one end protruding from the tip surface of the ground electrode main body 28 and a part of the other end embedded in the ground electrode main body 28 with respect to the ground electrode main body 28. However, the arrangement state of the noble metal portion 31 with respect to the ground electrode main body portion 28 is not limited to this. Therefore, for example, as shown in FIGS. 10 and 11, the tip portion of the noble metal portion 31 may be provided so as to protrude from the side surface portion of the ground electrode main body portion 28. At this time, as shown in FIG. 10, the whole area of one end of the ground electrode main body 28 may be embedded in the side surface of the ground electrode main body 28, or as shown in FIG. Only a part of one end of each may be embedded. By providing the noble metal portion 31 so as to protrude from the ground electrode main body portion 28, it is possible to suppress the heat of the spark (flame core) from being drawn by the ground electrode main body portion 28, and to further improve the ignitability. Improvements can be made.

  (F) Although not particularly described in the above embodiment, as shown in FIG. 12, the tip of the center electrode 5 may be tapered toward the direction of the axis CL1. In this case, since it is possible to suppress the heat of the flame from being drawn by the center electrode 5, it is possible to further improve the ignitability. Moreover, as shown in the figure, the center electrode 5 may include a columnar noble metal portion 32 made of a noble metal alloy at its tip. By providing the noble metal portion 32, it is possible to improve the spark wear resistance.

  (G) Although not specifically described in the above embodiment, as shown in FIG. 13, the center electrode 5 may include a noble metal portion 34 made of a noble metal alloy at a portion facing the tip opening of the shaft hole 4. Good. In this case, at the time of spark discharge transmitted through the insulator 2, it is possible to suppress the consumption of the side surface of the center electrode 5 and to further improve the durability. Note that the noble metal portion 34 may be provided only in a part (for example, a portion located on the ground electrode 27 side) without being provided in the entire region facing the tip opening of the shaft hole 4.

  (H) In the above embodiment, the case where the ground electrode 27 (the ground electrode main body portion 28) is joined to the distal end surface of the distal end portion 26 of the metal shell 3 is embodied, but a part of the metal shell (or The present invention can also be applied to the case where the ground electrode is formed by cutting out a part of the tip metal fitting welded to the metal shell in advance (for example, JP-A-2006-236906). Alternatively, the ground electrode 27 may be joined to the side surface of the distal end portion 26 of the metal shell 3.

  (I) In the above embodiment, the tool engagement portion 19 has a hexagonal cross section, but the shape of the tool engagement portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

DESCRIPTION OF SYMBOLS 1 ... Spark plug for internal combustion engines 2 ... Insulator as insulator 3 ... Metal fitting 4 ... Shaft hole 5 ... Center electrode 5G ... Outer peripheral surface 27, 27a, 27b ... Ground electrode 31, 32, 34 ... Precious metal Portion 33 ... Spark discharge gap 35, 35a as a gap ... Corner BP ... Projection shaft hole CL1 ... Axis EG1 ... First edge EG2 ... Second edge KG ... Virtual outer peripheral surface KS ... Virtual surface KT ... Virtual projection plane MB ... Chamfer SB ... Fine details SL1 ... First tangent SL2 ... Second tangent SP1 ... First contact SP2 ... Second contact TC ... Projection angle

Claims (10)

A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator having an axial hole extending in the axial direction and the central electrode provided in the axial hole;
A substantially cylindrical metal shell provided on the outer periphery of the insulator;
A grounding electrode extending from the tip of the metal shell, the tip being bent toward the center electrode,
A spark plug for an internal combustion engine having a gap between the center electrode and the ground electrode,
All the tip portions of the ground electrode are outside the virtual outer peripheral surface formed by extending the tip outer peripheral surface of the center electrode along the axial direction, and the tip in the axial direction from the virtual surface including the front end surface of the center electrode And exist on the side,
When the first shortest distance between the tip of the center electrode and the tip of the ground electrode is a, and the second shortest distance between the tip of the insulator and the tip of the ground electrode is b A spark plug for an internal combustion engine satisfying the following formula:
1.1 ≦ b / a ≦ 1.6   The spark plug for an internal combustion engine according to claim 1, wherein 1.5 ≦ b / a ≦ 1.6 is satisfied. The tip opening of the shaft hole and the corner closest to the tip of the center electrode among the tip of the ground electrode are projected onto a virtual projection plane orthogonal to the axis, and projected onto the virtual projection plane. The corners,
A contact point when a first tangent line is drawn from the first edge located at one end of the projection corner to the projection shaft hole that is the tip opening of the shaft hole projected onto the virtual projection plane is first. 1 contact,
When a contact point when a second tangent line is drawn to the projection shaft hole from the second end edge portion located at the other end of the projection angle portion is a second contact point,
The length L of the first contact and the second contact along the outer periphery of the projection shaft hole on the ground electrode side is 40% or more of the outer periphery length of the projection shaft hole. The spark plug for an internal combustion engine according to claim 1 or 2.   The length L of the first contact and the second contact along the outer periphery of the projection shaft hole on the ground electrode side is 50% or more of the outer periphery length of the projection shaft hole. The spark plug for an internal combustion engine according to claim 3.   The spark plug for an internal combustion engine according to any one of claims 1 to 4, wherein a tip portion of the shaft hole has a taper toward the tip end in the axial direction.   The spark plug for an internal combustion engine according to any one of claims 1 to 5, wherein a chamfered portion is provided at a tip opening portion of the shaft hole.   The spark plug for an internal combustion engine according to any one of claims 1 to 6, wherein a plurality of the ground electrodes are provided.   The spark plug for an internal combustion engine according to any one of claims 1 to 7, wherein the center electrode includes a noble metal portion at a tip portion thereof.   The spark plug for an internal combustion engine according to any one of claims 1 to 8, wherein the ground electrode includes a noble metal portion at a portion facing a tip edge portion of the center electrode.   The spark plug for an internal combustion engine according to any one of claims 1 to 9, wherein the center electrode includes a noble metal portion in at least a part of a portion facing the tip opening of the shaft hole.

Images